Dear Editor,

The spread of the coronavirus disease 2019 (COVID-19) pandemic has shown important spatial heterogeneity of in-hospital COVID-19 cases and deaths between countries and regions. Across metropolitan France, the healthcare system has been overwhelmed by the pandemic surge unequally over the regions, leading to the inability to provide care in areas with outpaced resources [1, 2]. In response, mass inter-regional transfers of critically ill patients have been organized. Distribution of evacuation and mutual-aid agreements were coordinated by Regional Health Authorities, and not as a typical day-to-day transfer system. Critical care transports were performed by specialized ground and aeromedical teams (including intensivists and emergency physicians). However, the evacuation of multiple critically ill patients raised important issues [3]. Overall, we do not know whether the mortality rates of transferred patients are closer to the ones observed in the sending regions, or conversely, in the host regions. The objective was to assess whether patients transferred from outpaced regions had better outcomes compared to patients with similar severity taken in charge in the regions with surges in patient volume.

We performed a cross-sectional study using data from the French hospital discharge database (HDD), exhaustive for all public and private hospitals. We included patients from the three metropolitan French regions that organized mass inter-regional transfers. Patients were included according to the following criteria: adults (≥ 18 years old), with invasive mechanical ventilation, admitted in intensive care unit (ICU) between 2020-03-01 and 2020-05-31, with ICD-10 diagnosis code of COVID-19. To identify whether inter-regional transfers were associated with the ICU case fatality, a multivariate logistic regression model was carried out, including variables with p < 0.2 in bivariate analysis. A descending stepwise process was used to select the final model. The Supplement details the methods.

Among the 6160 patients included, ICU-to-ICU inter-regional transfers were realized for 400 patients (6.5%) (Supplementary Fig. 1). Patients were less likely to be transferred if they had a higher Charlson comorbidity index or initial specific care supports such as prone position, renal replacement therapy, ECMO (Table 1 upper section). Age, sex, and SAPS II were not associated with the decision of transfer. Case fatality was 39.5% (2278/5760) for patients not transferred and 14.3% (57/400) for patients transferred. Among the factors significantly associated with case fatality, ICU-to-ICU inter-regional transfers were predictors of survival (adjusted OR: 0.26 [0.2–0.3], p < 0.0001) after adjustment on comorbidities and severity (Table 1 lower section).

Table 1 Factors associated with the decision of ICU-to-ICU inter-regional transfer of critically ill COVID-19 patients from French regions that organized mass interregional transfers and factors associated with case fatality in mechanically ventilated COVID-19 patients hospitalized in regions that organized mass inter-regional transfers (Bourgogne-Franche-Comté, Grand Est, Ile-de-France; March–May 2020)
Full size table

This study has limitations: (i) the study is from the “first wave”, therapeutic approaches have evolved since; (ii) healthcare systems vary across countries; thus our results should be extrapolated with caution; (iii) the lack of granularity of the database could be a limiting factor, but conversely it is an exhaustive real-life record of all patients hospitalized without initial selection bias.

The regions overwhelmed by the pandemic surge have experienced an unprecedented shortage of ICU beds and qualified ICU staff. We demonstrated that the benefit to remove patients from areas with outpaced resources was greatly superior to the risk of complication due to long-distance transfers of ventilated patients. In conditions with regional planning and trained teams [3], ICU evacuations are an appropriate solution to help manage the spatial dimension of the pandemic.